No, some of the parts stores will read the codes for you. OBD 1
Dodges have a built in flash read out you can activate on your own.
Grab a paper and pen, turn the key on off on off on it will start with
two digit number of 5 5 then a pause then the trouble codes will be
in a two digit form also, for example 1 flash 2 flashes would be a
code 12 and so on, the last code will be a 5 5 If you accidently go
too far and hit the crank the test will abort and you will have to start
over.
Diagnostic Trouble Code Descriptions and service hints.
Fault
11 No Crank reference
signal at PCM No Distributor reference signal detected during engine
cranking. Check the circuit between the distributor and PCM.
12 Battery Disconnect Direct Battery input to PCM disconnected
within last 50 ignition key-on cycles. Normal if battery has been
disconnected, otherwise check battery power and ground
connections.
13** No change in MAP
from start to run No difference seen between the engine MAP reading
and the barometric (atmospheric) pressure reading at startup.
Indicates a problem with the MAP sensor vacuum system.
14** MAP sensor voltage
too low or too high MAP sensor voltage output is outside the
acceptable range.
15** No Vehicle
speed sensor signal No signal received from the vehicle speed sensor
during road load operation.
17* Engine is cold
too long Engine temperature too high or too low while traveling.
Check coolant level, radiator cap, temperature sensor, and
thermostat.
21** O2S Stays at center
O2S shorted to voltage O2 sensor does not detect rich or lean
condition, or O2 sensor input voltage too high. DRB will indicate
which side with dual sensors. The O2 sensor signal should fluctuate
under normal conditions.
22** ECT sensor voltage
too high or too low Engine Coolant temperature sensor input out of
normal range. Check engine temperature sensor.
23** Intake air temp sensor
voltage too high or low Intake air manifold temperature sensor is out
of range. Check sensor.
24** Throttle position sensor
voltage too high or low TPS sensor is out of normal range.
25** Idle air control motor circuits A short is detected in one or more
of the idle air motor circuits.
27* Injector # control circuit Injector number # output driver circuit
does not respond to the control signal. Check the affected circuit.
31** EVAP Solenoid Circuit Short or open in the EVAP solenoid
circuit. Check for loose, broken, or shorted wire in the charcoal
canister purge solenoid wiring and connectors.
32** EGR Solenoid circuit Short or open in the EGR solenoid circuit.
Check for loose, broken, or shorted wire in the EGR valve wiring and
connectors. Possible air fuel ratio imbalance not detected during
diagnosis.
33* AC clutch relay circuit Short or open in the AC clutch circuit.
34* Speed control circuit or
speed control switch
always low or high An open or short in the speed control vacuum or
vent circuits. Speed control switch input above or below normal
range.
35 Radiator Fan low
speed relay circuit Open or short in the radiator fan relay wiring.
37** Torque converter clutch
solenoid CKT or
Trans temp sensor
too high or low Open or short in CKT wiring or connectors. Voltage
out of range at transmission temperature sensor input. See NOTE #1
below
41** Generator field not
switching properly Open or short in the generator (alternator) field
control (regulator) circuit. This indicates a problem with the charging
circuit and the fault is set when the battery voltage from the ASD
relay falls below 11.75 volts. Wiring, connectors, fuses, and the ASD
relay should be checked. A shorted battery cell can also trigger this
fault.
42* Auto shutdown
relay circuit Open or short in the ASD relay wiring or connectors.
43** Ignition coil circuit # Open or short in number # coil circuit.
Indicates that the ignition coil's peak primary circuit current is not
achieved with the maximum dwell time.
44* Battery temp sensor
volts out of range An open or short in the engine coolant temperature
sensor circuit or a problem in the PCM's battery temperature circuit.
45* Trans OD
solenoid circuit Transmission OD solenoid circuit failure. Open or
short in the transmission overdrive solenoid circuit.
46** Charging system
voltage too high Battery voltage sense input above target charging
voltage during engine operation. Computer is indicating that the
battery voltage is not being regulated.
47** Charging system
voltage too low Battery voltage sense input above target charging
voltage during engine operation. Also, no significant change in
battery voltage was detected during a test of the generator output.
51** System lean L-Idle
Adap at rich limit
or lean R-Idle
Adap at rich limit O2 sensor signal indicates lean air/fuel ratio during
engine operation. The computer ran the mixture to the rich limit of
programming, but the O2 sensor still indicated a lean condition. L or
R indicate left or right side O2 sensor. Fuel pressure problems can
lean the mixture and set this fault.
52** System rich L-Idle
Adap at lean limit
or rich R-Idle
Adap at lean limit O2 sensor signal indicates rich air/fuel ratio during
engine operation. The computer ran the mixture to the lean limit of
programming, but the O2 sensor still indicated a rich condition. L or
R indicate left or right side O2 sensor. Faulty ignition components,
high or low fuel pressure, or leaking injectors can set this fault.
53* Internal PCM failure
or PCM SPI comm
failure An internal PCM failure or PCM communications failure has
been detected.
54* No cam sync signal
at PCM No fuel sync (camshaft signal) detected during engine crank.
No camshaft position sensor signal was received from the distributor.
Problem with the distributor synchronization circuit.
55 N/A End of message code. A DTC 55 is used to end all DTC
messages. This code does not show on the DRB tool and indicates a
completion of the stored codes on the Malfunction Indicator Lamp
(check engine lamp).
62* PCM failure
SRI miles not stored Unsuccessful attempt to update Service
Reminder Indicator miles in the PCM EEPROM (memory).
63* PCM Failure
EEPROM write denied Unsuccessful attempt to write and EEPROM
location by the PCM. Controller failure, check the PCM. This code
can be set when attempting an unauthorized reprogram of the PCM.
71** Aux 5V signal
voltage low The auxiliary 5 volt supply output voltage is low. The 5 volt
output signal is not reaching the required voltage level.
72** Catalytic Converter
efficiency failure The catalytic converter is not converting emissions in
the proper ratio.
Fault codes with * = Check engine lamp may not illuminate at all
times if this code was recorded.
Fault codes with ** = Check engine lamp will illuminate when the
engine is running if this code was recorded.
Fault codes with red stars * or ** vary from above, depending on the
model year.
NOTE #1 - From the 1995 TRUCK (Ram) manuals: the trailer towing
package includes a transmission coolant temp sensor while the
standard package doesn't. The fault code detection system is
probably the same for both models. This could cause the low (no)
voltage indication....no sensor to send any voltage.

I am having problems with my 94 ram 1500. the check engine light is on
and the codes that flash are 12, 21. It idles rough and didn't think that the
O2 sensor had much to do with it and found that a common problem is
the iac sensor. I replaced that and it still idles rough. now when i check
the codes it flashes 21 twice??? any recommendations?